This invention relates to household refrigerators and is more particularly concerned with a combination refrigerator, that is, a refrigerator including a freezer compartment on top and a fresh food compartment below, both of which are cooled by circulation air from the two compartments over a single evaporator employing a single fan to accomplish the circulation. This invention relates to an air flow control and method of controlling the circulation of air to thus control the temperature of the refrigerator compartments.
Combination refrigerators, including a single evaporator and a single fan for circulating air from the freezer and fresh food compartments over the evaporator are well known. In the operation of such refrigerators, a major portion of the refrigerated air from the evaporator is directed into the freezer compartment while a smaller portion is directed into the fresh food compartment. In addition to the cost advantage resulting from the employment of a single evaporator and a single fan for refrigerating two separate compartments, such refrigerators have the additional advantage of permitting automatic defrost of the evaporator which is normally contained within an evaporator chamber outside of or separate from both of the storage compartments without significantly disturbing the temperatures of those compartments.
Various means have been used or proposed for providing temperature control employing a single thermostat for maintaining the two compartments within their desired operating temperature ranges. One such means of control is described in U.S. Pat. No. 3,320,761. Generally, thermostatic control of the evaporator is achieved by using an air temperature sensing element in the warmer fresh food compartment. An adjustable air flow divider proportions the flow of air cooled by the evaporator, through the freezer and fresh food compartments, to thus provide the desired temperature differential between the freezer and fresh food compartments.
The air flow divider is adjusted, however, during a particular ambient atmospheric condition, for example, 70.degree. F., the satisfactory control may not be achieved at a higher ambient atmospheric temperature, for example, 100.degree. F., due to the unequal rate of heat flow into the fresh food compartment. In the higher ambient temperatures, the heat flow from the ambient into the fresh food compartment is higher relative to the freezer compartment than in low ambient temperatures. This can be remedied by increasing the ratio of cold air into the food storage compartment in higher ambients. Such changes in usage conditions may be accommodated by including a manually-operable fresh food compartment air flow adjustment. One such control system is shown in U.S. Pat. No. 3,656,314 wherein there is described an air conduit having branches that provide separate cooling air discharge into the freezer compartment and has a temperature sensing means disposed in the conduit for controlling the temperature. The temperature sensing means, however, is located in the cold air stream upstream of a damper that controls the amount of cold air being introduced into the fresh food compartment. With this arrangement, the temperature sensing means will give a constant freezer control response rather than a constant fresh food response since it is most heavily biased by freezer air temperature. There is an adjustable control for regulating the amount of cold air passing into the fresh food compartment. However, with such an arrangement, the fresh food temperature is inadvertently affected which can result in the temperature being either too high or too low in the fresh food compartment.
It is highly desirable to control the temperature in the refrigerator so that the temperature in the fresh food compartment stays relatively constant and the ratio of the temperatures in the freezer and fresh food compartments is changed. By our invention, these desirable characteristics of a refrigerator air flow system are provided.